AVS 50th International Symposium
    Plasma Science and Technology Tuesday Sessions
       Session PS-TuM

Paper PS-TuM7
In-situ Processing Memory Effects for Confined vs. Unconfined Plasmas

Tuesday, November 4, 2003, 10:20 am, Room 314

Session: Plasma Diagnostics: Processing
Presenter: E.A. Hudson, Lam Research Corp.
Authors: E.A. Hudson, Lam Research Corp.
R. Annapragada, Lam Research Corp.
D. Keil, Lam Research Corp.
K. Takeshita, Lam Research Corp.
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In the fabrication of integrated circuits there is a growing trend towards performing several etch steps in a single pass through an etch tool. This in-situ processing approach reduces production costs and cycle times, but presents technical challenges because it requires the sequential use of very different plasma chemistries in the same reactor. An important example is the use of a polymerizing fluorocarbon-based plasma to etch patterns into silicon dioxide or organosilicate films, followed by oxidizing plasmas to remove the remaining photoresist film. Residual fluorocarbon polymer, left on chamber surfaces by the etch step, is attacked under oxidizing conditions, releasing fluorine-containing species which may have harmful effects on the wafer structures. This paper compares the "fluorine memory" effect for unconfined vs. mechanically confined capacitively-coupled RF discharges. Diagnostic measurements focused on plasma properties, chamber surface cleaning efficiency, and wafer-level results. Optical emission spectroscopy was used to detect atomic fluorine in the plasma during the photoresist strip step. Fluorine was found to persist much longer in the case of the unconfined plasma. The impact of residual byproducts at the wafer was evaluated from silicon dioxide loss and from changes in feature dimensions. Results indicate that use of a mechanically confined plasma greatly reduces "fluorine memory" effects during the photoresist strip step, compared to the unconfined configuration. This is attributed to the reduced gas residence time and more efficient cleaning of chamber surfaces in the confined configuration.